chore(*): get rid of Bower in favor of Yarn aliases & checked-in packages

Bower was used to install multiple versions of jQuery which is now handled
using Yarn aliases. The remaining two packages, closure-compiler and
ng-closure-compiler were installed from zip files which is not supported by Yarn
(see https://github.com/yarnpkg/yarn/issues/1483); the first of them exists
on npm as the google-closure-compiler but only versions newer than we used are
published and they don't work with ng-closure-compiler so - instead - both were
checked in to the repository.

Fixes #16268
Fixes #14961
Ref yarnpkg/yarn#1483